Tools/nativelib/rwlock.c

   1 /*
   2  * Acess2 libnative (Kernel Simulation Library)
   3  * - By John Hodge (thePowersGang)
   4  *
   5  * rwlock.c
   6  * - Read/Write locks
   7  */
   8 #include <acess.h>
   9 #include <rwlock.h>
  10 #include <events.h>
  11 #include <threads_int.h>
  12
  13 // === CODE ===
  14 int RWLock_AcquireRead(tRWLock *Lock)
  15 {
  16         SHORTLOCK(&Lock->Protector);
  17         while( Lock->Level < 0 || Lock->WriterWaiting )
  18         {
  19                 // Wait
  20                 tThread *me = Proc_GetCurThread();
  21                 me->ListNext = NULL;
  22                 if( Lock->ReaderWaiting )
  23                         Lock->ReaderWaitingLast->Next = me;
  24                 else
  25                         Lock->ReaderWaiting = me;
  26                 Lock->ReaderWaitingLast = me;
  27                 SHORTREL(&Lock->Protector);
  28                 Threads_WaitEvents(THREAD_EVENT_RWLOCK);
  29                 SHORTLOCK(&Lock->Protector);
  30         }
  31         Lock->Level ++;
  32         SHORTREL(&Lock->Protector);
  33         return 0;
  34 }
  35
  36 int RWLock_AcquireWrite(tRWLock *Lock)
  37 {
  38         SHORTLOCK(&Lock->Protector);
  39
  40         while( Lock->Level != 0 )
  41         {
  42                 tThread *me = Proc_GetCurThread();
  43                 me->ListNext = NULL;
  44                 if( Lock->WriterWaiting )
  45                         Lock->WriterWaitingLast->Next = me;
  46                 else
  47                         Lock->WriterWaiting = me;
  48
  49                 SHORTREL(&Lock->Protector);
  50                 Threads_WaitEvents(THREAD_EVENT_RWLOCK);
  51                 SHORTLOCK(&Lock->Protector);
  52         }
  53         Lock->Level = -1;
  54         SHORTREL(&Lock->Protector);
  55         return 0;
  56 }
  57
  58 void RWLock_Release(tRWLock *Lock)
  59 {
  60         SHORTLOCK(&Lock->Protector);
  61         if( Lock->Level == -1 || Lock->Level == 1 )
  62         {
  63                 // Last reader or a writer yeilding
  64                 // - Yields to writers first, then readers
  65                 if( Lock->WriterWaiting )
  66                 {
  67                         Threads_PostEvent(Lock->WriterWaiting, THREAD_EVENT_RWLOCK);
  68                         Lock->WriterWaiting = Lock->WriterWaiting->ListNext;
  69                 }
  70                 else
  71                 {
  72                         while(Lock->ReaderWaiting)
  73                         {
  74                                 Threads_PostEvent(Lock->ReaderWaiting, THREAD_EVENT_RWLOCK);
  75                                 Lock->ReaderWaiting = Lock->ReaderWaiting->ListNext;
  76                         }
  77                 }
  78                 // Nobody to wake, oh well
  79                 Lock->Level = 0;
  80         }
  81         else if( Lock->Level == 0 )
  82         {
  83                 // ... oops?
  84         }
  85         else
  86         {
  87                 Lock->Level --;
  88         }
  89         SHORTREL(&Lock->Protector);
  90 }
  91